My speedometer is off. The car was a 17" stock wheels. Same wheels are on there. My speedo tells me im doing 30 when im going 30 and 35 at 35. but it tells me im going 45 when im really doing 50. at 50 im doing 57. At 60 im really going 73. and ive not had anyone help me after that.
what could be causing this

 

did you put different size tires, like went from a 30 sidewall to a 50 or something?

 

idk the guy who had it before me had 17 cobra rims on there with 17/40/275 all around. the cars vin checks out that it had 17 stock rims

 

The only other thing I can think of is that maybe he put different gears in it and didn't recalibrate thecomputer or put new speedogears in. You might just take it to a performance shop and see if they can verify how much its off then they can set your computer so it's accurate.

 

alright thanks... now then to a performance shop>> wherever one is around here XD

 

An easier way to find out is to jack up the rear of the car (use the diff to jack it up) and rotate the tires. See how many times the driveshaft rotates in comparison to one revolution of the tires.

 

+1 Just make sure that you mark a place on the driveshaft and on the tire..

 

if he had lower gears then the speedo would say he'sgoing faster than he really is, not slower.

 

If you have a handheld tuner you can update your revolutions per mile. Go to this website (tire size calculator) http://www.csgnetwork.com/tireinfo4calc.htmland put in your tire and rim size. Mine are 255/40/17 which seem to be slightly lower than the stock 245/45/17s.When I did my calculation it said that my tires travel 805.1 revolutions per mile.I then changed that parameter on my handheld (SCT xcalibrator2) and now my speedo is correct.

 

Maybe it once had gears and the stockers were put back in place when the car was sold.